MAGNETIC SURVEY OF GREAT BRITAIN. 169 



Hence if ST' denote the small correction in the value of T', and 

 8 h the corresponding correction of //, 



h ~ T' 



To apply this in the present instance, we have 



I. («) L (b) 



s s 



Mean of separate observations . . . 243*43 293*18 

 Mean of initial and final results . . 243-29 293-06 

 Correction of T', or ST' +0-14 +0-12 



Resulting value of -r* + -0011 + -0008 



n 



The corrections here obtained are applied to all the results 

 of the series (Aug. 19, to Sept. 15, 1835) in Table LXVIII. 



Values of the Intensity at the Base stations. — The following 

 is a summary of the comparisons of the horizontal intensity in 

 London, Dublin, and Limerick, as contained in Table LXIX. 



Horizontal intensity in Dublin, referred to London : 



Horizontal intensity in Limerick, referred to London : 



July, Aug. Sept. 1S34. Cyl. S h Int. = -9396 



July, 1835. — S /j — = -9470 



Jxily, August, 1835. — Re — =-9461 



July, August, 1835. — Rrf —=-9513 



Mean = -9460 



